Stop draining once the defenders are out of trump (declarer's view)
'Me' at the bottom is the viewpoint player; P2–P5 are the other four seats.
Setup
Mighty Basics Replay. This game is from the declarer's view: when to stop the trump drain. Trump (giruda) is ♠, contract 13. Mighty is ♦A, and P2, who holds it, is my Friend. I hold the Joker and four trumps, and I emptied my hearts in the exchange. Watch when the defenders' trumps are all drawn, and the switch to stop leading trumps once they are.
Trick 1
Trumps can't be led on the first trick, so I opened with the ♦K. The only card above the ♦K is the Mighty, and it's in my Friend's hand, so it's effectively a boss card.
Trick 2
I started a trump drain with a low ♠2. My Friend took it with the Mighty and was revealed, and P5's spade void came to light.
Trick 3
My Friend continued the drain with the ♠4. P3 held on with the ♠K, but playing last, I covered with the ♠A.
Trick 4
This time I led the Joker and called spades. A trump drain with the Joker. Counting cards, only two trumps remain outside: ♠Q and ♠J.
Trick 5
When I led a low ♠5, my Friend won with the ♠Q, and P3's last trump, the ♠J, was pulled out. The defenders' trumps are all gone. This is where the trump drain stops.
Trick 6
My Friend led the ♥4. The defenders seemed to be winning with ♥A, but playing last, I ruffed with the ♠7 I had saved. Had I spent that 7 on the drain, this ruff wouldn't have happened.
Trick 7
Now there are no trumps left in the game. I led my non-trump boss, the ♦Q, took 3 points, and made the contract at 13.
Trick 8
I led the ♦2, and it won. The only diamonds left are my ♦8 and ♦2, and there's no trump to ruff with, so even the ♦2 is as good as a boss.
Trick 9
Once more with the ♦8. My Friend loaded the ♥Q.
Trick 10
My last card, the ♣5, lost to P5's ♣A, and that gave the defenders their only 2 points of the game.
Result
18:2, comfortably over the contract. A trump drain is only a means to pull the defenders' trumps. Once there's nothing left to pull, stop at once, save your remaining trumps for ruffing, and go collect points with non-trumps. You can step through this game yourself in the Basics Replay section of Mighty Korea's school (mightykorea.com).