The HAYWARD S310T2 sand filter shown here is common to this area.
Often the valve is plumbed directly to the pool plumbing and the lines have to be cut to remove the valve from the top of the filter to service the filter. I recommend adding unions at that time so the valve can be removed for service in the future.
Any repairs to the internal parts of this filter require that the sand be removed before servicing.
If sand and or debris is coming from your pool returns, your multiport valve gasket is damaged, or there is damage to the internal parts of your filter.