Ciao Gianni,

I do not know if this was the correct thing to do...BUT...I used a form of acid that was some solution of Hydrochloric acid on BeBe's aft tank valve. I poured it in the deck pump-out opening, let it sit for about 15-20 seconds, then worked the valve handle back and forth. I repeated twice, then flushed with baking soda and water solution to neutralize the acid. I believe once you get it working freely you may be able to pump some lithium grease into the valve to lubricate it.

If your tank is full, you will have to have it pumped out before you try above.

Hope this helps.

Bill
BeBe, SM2k, #387
Currently Fethiye, Turkey