Vacuum to waste problem

[AMH]

When I vacuum to waste the pool shed where the filter and pump are located flood. Also the area outside by the pool.
Im assuming a blockage?
The pipe I’m guessing leaves the filter and is underground.
Is there a T junction type pipe underground where one side goes to return to pool for normal filtration and the other goes to waste?
If I dig a hole will I find the pipe? How far down should so dig?
What should I look for ? Will there be a blockage ?
The filter and pool works great. But since I owned the property its always floods when set to vaccum to waste.
Advice please.

[Teapot1]

There is a waste port on the multiport valve (if fitted to your filter). The water should exit there and then off to where ever it goes to. Not normally a 3 port valve or T in line but some people fit a valve to their waste line to stop the multiport leaking, water for return comes from a different port on the multiport valve.

[Denniswiseman]

Maybe some images of your setup