Pool pump water level drop when switching to main drain


New member
Aug 19, 2020
Pearland, TX
Hi everyone,

I am a new pool owner and figuring out all of my equipment. I have a valve that allows me to switch between the skimmer baskets and the main drain (and pool vacuum line). My pipes are not labeled, so I am switching it around to try and map it all out. But I noticed when I switch it to the main drain line only, closing the skimmer baskets, the water level in the pump drops significantly and it sounds like the pump is running louder. Opening the valve partially to allow the skimmer lines back in solves the problem and the pump completely fills with water again.

My question is really is this normal? Or is this something I need to be concerned about.

Below is a photo of the equipment so you can see the valve leading to the pump.

Thanks so much!

EDIT: Another semi-related question I have about this equipment. Can I use that hose valve above the pool pump to drain water from the pool? We have head very heavy rains and I would like to lower the water level a little bit if possible.

Last edited:


Gold Supporter
TFP Guide
Jul 21, 2013
Northern NJ
Yes, you can use the hose valve above the pump to drain some water from the pool. But you need to watch the draining so that your pool pump does not run dry and get damaged. We suggest not putting an expensive pool pump at risk of damage and using a submersible utility pump to drain a pool when necessary.

What you are seeing and hearing is the pump cavitaing because the main drain alone can not provide enough water to the pump. It takes some water flow from the skimmers with the main drain to satisfy the pumps suction requirements. This is normal.