So many times I paid my son's storage, retrieved his belongings...and it never ended well. In hindsight I would have just let him pay the consequence of losing anything he could sell for drugs.
I am guessing how this might play out for you and your son...tell me if I'm close...he had $1800 last week and could have arranged to get his piano. If he blew the money on drugs, what difference does it make if you get his things...he will find out, insist they are his, pawn them and away he goes again...more drug money.
One mama to another, let go of trying to fix anything including losing his things. If he wants to get clean, he knows where help is and he won't need a piano for that.
Do what brings your heart peace. Whatever you choose, I'm walking with you.
Hugs