If you mean PTFE thread tape then I'm using It right now at work on a 200bar ( about 3000 psi ) system, which stops small leaks, but its got to be replaced/ re-applied each time you break the joint/ fitting.
The trouble is with the P1D is that you turn the head or threads to turn on and off, so this action will push the tape off the threads and leave them bare.
I nyogelled my orb raw ns, ( same threaded twisty operation) and threw it in the bath with my son for 20 mins and that was ok, but i dont know about at the bottom of the swimming pool, there is a bit more preasure there, but he never turned it on or off, so I dont know about weather it would survive or not.
If I realy wanted to take a P1D light underwater, i'd nyogel all point the water could get in, and then probably put a turn of electrical tape around the join, but that doesnt stop the bezzle leaking, So the best bet would be to buy a rated dive light, or risk it and find out.
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