Problem with vacuuming to waste

[amin36]

Guys

Today I went to a client's pool and he asked for me to teach him how to manually vacuum the pool.

He used flocculent and it all sat at the bottom of the pool and I wanted to vacuum the water to waste.

He didn't have a vacuum plate so I directly attached the vacuum head to the skimmer with a hose connector.

So I closed the bottom drains and while the sand filter was running on filter mode I primed the hose using one of the returns.

I had a very good suction so I stopped the pump and put the filter on waste. When I started the pump I had a very weak suction.
I couldn't figure out what is happening so while the filter was on waste mode I tried different ways of priming the hose and still no results
I even checked to see for usual problems while manually vacuuming the pool but there was nothing wrong.
After all the suction was great when priming the hose on filter mode.

Any ideas what is going on here?

 

[Texas Splash]

From your description it sounds as though when you stopped the pump to switch settings, your lost prime in both the pump pot and apparently through the vacuum hose itself is that correct?

 

[amin36]

From your description it sounds as though when you stopped the pump to switch settings, your lost prime in both the pump pot and apparently through the vacuum hose itself is that correct?

Yes but in other pools when i stop the pump i am not losing prime.

 

[Texas Splash]

For water to flow about of the lines would indicate there's am air leak somewhere. If everything is air-tight, the water should stay in place. Just like holding your thumb over the end of a full straw.