Another direction to consider, Yuri...
Having just put 13 gallons of stout in a 15.5 yeast brink-basically a sanke container with a tri-clamp fitting on top. The ones I saw was with the large style fitting, like maybe 3", instead of the more common smaller one that is the usual size for HB'ers. Breweries have a modified sanke spear with the same size fitting that is used with the tri-clamp and washer to keg wash it on the keg washing system. If you were to modify a sanke spear to dispense with a sanke tap, you could have a multiple use 15.5 gallon container. Just make an adapter that goes from large tri-clamp (clover?) to sanke...
With a tri-clamp fitting and valves, we pitched yeast right into the brink, from right under a huge conical fermenter, on top of the wort, and then used a hose with another tri-clamp to serve as a 1/2" blow-off hose...
You wouldn't have to have the tri-clamp valves, but just use those fittings on standard valves, you'd have a versatile piece of equipment.
I think on Brewboard there is a guy who welds sanitary SS for a living, and started selling nice tri-clamp kits for way cheap. Can't say who it is....
Sorry, don't know how to directly post a hosted image...