Stupid question plumbing

[South Carolina reef]

I'm installing a new UV on my existing tank. I plan on running it off of my return pump. My stupid question is...o ce I cut the power and stat to replumb into the uv will the water drain from the DT into the sump? If so how much. I assume only a couple gallons once it got below the overflow correct

 

[cmaxwell39]

It depends. If the lowest point in your plumbing system in the display tank is your overflow, then yes it would drain down to the level of your overflow teeth. If you have return plumbing that extends into the tank deeper than the overflow teeth and you do not have a siphon break hole drilled, your display will drain until the siphon is broken,

Do you have a check valve installed? If not, then anytime you lose power or shut your return pump off the display will drain down until the siphon has been broken. Even if you have a check valve installed, you should test the drain back without it so that you are sure your sump can handle it if the check valve ever fails.

 

[EeyoreIsMySpiritAnimal]

I'm installing a new UV on my existing tank. I plan on running it off of my return pump. My stupid question is...o ce I cut the power and stat to replumb into the uv will the water drain from the DT into the sump? If so how much. I assume only a couple gallons once it got below the overflow correct

Your tank already drains a certain amount into the sump when the pump is turned off.
A siphon won't magically restart just because you remove the pipe...

 

[South Carolina reef]

It depends. If the lowest point in your plumbing system in the display tank is your overflow, then yes it would drain down to the level of your overflow teeth. If you have return plumbing that extends into the tank deeper than the overflow teeth and you do not have a siphon break hole drilled, your display will drain until the siphon is broken,

Do you have a check valve installed? If not, then anytime you lose power or shut your return pump off the display will drain down until the siphon has been broken. Even if you have a check valve installed, you should test the drain back without it so that you are sure your sump can handle it if the check valve ever fails.

I have a hole drilled in the return pipe 90 yes