I have a Sta-Rite T-240BP-1 sand filter.

A couple weeks ago I replaced the plug/gasket assembly without any problems.
I also replaced the O-Ring and washers on top of the plug (washers had corrosion)
I noticed that I removed 5 washers, but instruction manual indicates 3. (one below spring, 2 above) I installed 3 per manual. I think these washers simply prevent the spring from wearing against adjacent parts.

In normal filter position, water is goes on top of sand is filtered and collected by the laterals, up the centre pipe and out to the pool. Is there anything to prevents water from leaking from above the sand to directly to the pipe.

While there is nothing shown in the manual, I was expecting to see some sort of O-Ring at the top of the centre pipe or internal to the valve cavity that the pipe sits in. Is this normal, or am I missing a seal.