OP,
Most anything can be done in a house if you are willing to pay the cost?
Perhaps you dont understand what's meant by tanking? No reason that you should if you dont work in the trades.
To correctly tank what you show might be complicated, & expensive.
The possibility of any method of tanking failing is a possibility.
If you are actually talking about boxing-in (not tanking) the "cluttered" corner in the pic then it would be a straight forward job?