The best way to clean and sanitize your stainless brewing equipment

One of the useful features of the BREWHA BIAC is that boiling can occur inside the fermenter which makes sanitation a snap—the heat of the boil will sanitize the fermenter so there is no need to chemically sanitize the vessel. All that is needed is to clean the fermenter out well with water and a soft cloth after the beer is removed, disassemble and clean out the valves (the article at this link discusses how to disassemble the valves), and it is ready to go for the next batch.

However, when having just purchased a new BREWHA vessel (including the 3-in-1 and 4-in-1) or if beer stone builds up after several brews, deeper cleaning is necessary. With the new vessels it is important to remember that the vessel comes direct to you from the shop where it is hand-made. This means that there could be a small amount of oil or welding stains on the vessel and there could be welding material or polish inside the jacket so a thorough cleaning of your vessel and flushing out of your jacket should be completed before starting to brew. (It is especially important to clean out your jacket well if you will be using it for providing sparge water during mashing.) 

In order to deep clean your vessel we couldn’t make a better recommendation than John Palmer already has in his book How to Brew. In his book John states the following:

Cleaning Stainless Steel and Aluminum
For general cleaning, mild detergents or percarbonate-based cleaners are best for steel and aluminum. Bleach should be avoided because the high pH of a bleach solution can cause corrosion of aluminum and to a lessor degree of stainless steel...
...the corrosion inhibitor in stainless steel is the passive oxide layer that protects the surface. The 300-series alloys (a.k.a. 18-8 alloys) commonly used in the brewing industry are very corrosion-resistant to most chemicals. Unfortunately, chlorine is one of the few chemicals to which these steels are not resistant. The chlorine in bleach acts to destabilize the passive oxide layer on steel, creating corrosion pits. This type of attack is accelerated by localization and is generally known as crevice or pitting corrosion.
Many brewers have experienced pinholes in stainless-steel vessels that have been filled with a bleach-water solution and left to soak for several days. On a microscopic scale, a scratch or crevice from a gasket can present a localized area where the surface oxide can be destabilized by the chlorine.  The chlorides can combine with the oxygen, both in the water and on the steel surface, to form chlorite ions, depleting that local area of protection. If the water is not circulating, the crevice becomes a tiny, highly active site relative to the more passive stainless steel around it and corrodes. The same thing can happen at the liquid surface if the pot is only half full of bleach solution. A dry stable area above, a less stable but very large area below, and the crevice corrosion occurs at the waterline. Usually this type of corrosion will manifest as pitting or pinholes because of the accelerating effect of localization.
A third way chlorides can corrode stainless steel is by concentration. This mode is very similar to the crevice mode described above. By allowing chlorinated water to evaporate and dry on a steel surface, those chlorides become concentrated and destabilize the surface oxides at that site. The next time the surface is wetted, the oxides will quickly dissolve, creating a shallow pit. When the pot is allowed to dry, that pit probably will be one of the last sites to evaporate, causing chloride concentration again. At some point in the cleaning life of the pot, that site will become deep enough for crevice corrosion to take over and the pit to corrode through.
It is best to not use bleach to clean stainless steel and other metal. There are other cleaners available that work just as well without danger of corrosion. The percarbonate-based cleaners like PBW are the best choice for general cleaning.
If you have a particularly tough stain, liked burned malt extract, then you may need something stronger. There are oxalic acid based kitchen cleansers available at the grocery store that are very effective for cleaning stains and deposits from stainless. They also work well for copper.  One example is Revere Ware Copper and Stainless Cleanser, another is Bar Keeper's Friend, and another is Kleen King Stainless Steel Cleanser. Use according to the manufacturer's directions and rinse thoroughly with water afterwards.

For keeping your equipment clean, we strongly recommend cleaning immediately after brewing (or with the fermenter, as soon as you transfer beer out) as residue will be much easier to remove before it dries. Use a soft cloth or plastic scrub brush that is recommended for stainless steel and don’t use steel wool to scrub the pot as this will scratch the mirror polish finish (although 100% copper scrub brush such as made by Chore Boy is very helpful to clean scorched or caramelized sugar off the heating element). It is also recommended to disassemble the valves when cleaning and wipe out any visible sediment (heat from the boil will take care of the rest), and take care not to stretch the silicone lid or valve gaskets as they may deform.

The best sanitizer is heat (being able to heat sanitize your fermenter is one of the principle benefits of the BIAC). If chemical sanitation is necessary or preferred, we recommend STAR SAN. Since the lid is generally off during boil, it may be beneficial to put the lid on the fermenter for the last couple minutes of boil to let the steam heat it up (be careful to allow steam to escape and that foaming up does not occur), and/or to spray a little Star San on the lid, exit ports and through the blow off tube. Acid 5 and PBW can be used effectively to remove beer stone (recirculate in warm/hot water for 30 minutes with the CIP assembly).

Also, it is important to note that 'stainless' steel is a bit misleading as it doesn't mean it will never stain or rust. It should actually be called 'harder-to-stain' steel. The following is from a section by General Electric on taking care of stainless steel.

The largest single component of stainless steel is steel. Steel will rust. The chromium in stainless steel when exposed to oxygen in the atmosphere forms a thin invisible layer called chromium oxide. This invisible layer covering the entire surface gives stainless steel its ability to resist stains and rust. If this layer is damaged rust is formed on the surface at the point of that damage. The good news is, with a little cleaning and care the chromium oxide layer is self­-healing...

Stainless steel and the chromium oxide layer actually thrive on proper cleaning. For everyday cleaning of non­oxidized soils, dust, dirt and fingerprints, a mild soap/detergent (dish detergent) and warm water solution should be used. Use the solution to remove the soil, rinsing with fresh water and a clean cloth, and dry completely.

To clean spots (cosmetic) from the stainless we recommend using Bar Keeper's Friend, and it also works well to remove rust spots and to 'heal' areas that might be open to rust. A periodic full vessel cleaning with Bar Keeper's Friend (or another acid) can also help preserve the entire fermentor and is recommended for getting greatest longevity from your stainless steel.

Instructions on care of stainless can be found at the following link to the Specialty Steel Association of North America's guide to 'Care and Cleaning of Stainless Steel'.

A detailed discussion on care of stainless is the Nickel Development Institute's 'Cleaning and Descaling of Stainless Steel'.

Palmer also has a more in depth discussion about removing rust and how to passivate stainless steel at this link.