Leaking ABS P-trap union

I removed an adjustable ABS P-trap under a bathroom sink to clean out the sink overflow with a plunger. I've got the P-trap back on now, but it's leaking at the union-type connection between the two halves of the P-trap. I've tightened that joint, but it's still leaking. I'm concerned that more tightening will do more harm than good.

I've put a pail under the trap to catch the water leakage, but the tenant isn't gonna want to be without a bathroom sink for any length of time, and I'm seeing that one of the Brasscraft shut off valves is close enough to the top portion of the trap that it'll be in the way when I'm unscrewing that top portion from the threaded brass elbow in the wall.

So, I just want to stop this leak for now. I can replace the P-trap when this tenant eventually vacates (when it doesn't matter if the sink can't be used for a while).

I'm thinking of just applying some silicone caulk to the two sealing surfaces in that union-type joint, but I figured I'd ask in here if anyone knew of anything better to use than silicone caulk?

A p-trap has three swivel fittings. Loosen all three.
Then tighten the middle swivel first; and then the ends.

The middle nut "always" is tightened first.

If this is a sch. 40 glued trap with a middle union nut, then they usually leak after they have been disturbed.

I expect I probably did tighten the middle one first, but I'll try again, this time being sure to tighten the middle one (that is the union) first.

If that doesn't work, then I'm going to silicone it.

Thanks for the responses.

quote; If that doesn't work, then I'm going to silicone it.

You won't be the first person to do it, just don't expect to take it apart without sawing it, however.

Worse yet is when someone glues it

No, I wouldn't cement the two halves together.

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