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:
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. For passivating a larger area, or in areas that are hard to reach (such as between wedge wire or in jackets) circulating for 30-60 minutes with a 10% citric acid solution (other acids can be used but citric acid is food safe and readily available) at 65C/150F and letting the area fully air dry for 12 hours before rinsing is generally all that is needed to mend any damaged areas to help preserve the fermentor and get the 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.