A multi-port should have filter, backwash, rinse, waste and hopefully recirculate settings. When I said BYPASS, I actually meant recirculate, to bypass the filter media. IMHO you have an obstruction after the pump, and a system leak somewhere. Do you have a pressure gauge, and if so what are the readings? Who replaced the sand and other parts, and were the correct replacements and amounts used? Are all of the pool returns open, the eyeballs weren't inadvertently turned sideways? Was the new filter sand properly backwashed before filtering?
When the pump shuts off, system pressure should dissipate through the filter and returns with very little back-flow towards the pump strainer basket-skimmer/drains. Water in the system will stay where it is, unless you allow air in, then it will drain to low points. Here are some Hayward sand filter tips that apply to most sand filters:
Hayward Sand Filter Operation Tips
SHUT OFF PUMP - Turning the filter Control Valve handle while water is being pumped through the filter can damage the valve and possibly other equipment as well. So Always shut off the system's pump before switching valve positions. Then, when turning the valve, be sure to fully depress the valve handle to prevent damaging the valve seal gasket.
PERIODIC (NOT FREQUENT) BACKWASHING - A little-known fact is that a sand filter operates most efficiently during mid-cycle. Debris trapped in the sand bed actually help the filter work better - so frequent backwashing reduces efficiency. Sand filters should only be backwashed when the filter has collected so much debris that it begins to restrict water flow and increase water pressure.
USE PRESSURE GAUGE - The use of a pressure gauge with sand filters is very important because the filter should not be backwashed until water pressure has risen 5 - 10 PSI (see owner's manual per unit) due to accumulated debris in the filter.
WATCH BACKWASH CLOSELY - Backwashing can waste 50 to 300 gallons of water, so pay attention - this water has chemicals you paid to put in the pool, not the street. Backwash until the waste line water or site-glass water on the side of the valve becomes clear.
NEW POOL CLEANING - Do not vacuum a new pool with the filter in the backwash mode, as this could plug up the laterals at the bottom of the filter with dust from the new pool surface.
VERIFY FLOW RATE - If the filter's recommended flow rate is exceeded, a shafting effect (tunneling) will take place in the sand, allowing debris to bypass the sand's intended filtration effect.
Hayward Sand Filter Repair Tips
CONNECTING PIPES TO THE VALVE - We see a lot of cracks created by installers incorrectly attaching a pipe to the VAri-Flow valve. For a slip valve connection, use regular PVC glue to attach the pipes. However, for threaded valve connections, use Teflon tape or Permatex #2 so that a flexible non-permanent seal is created. Also, the use of unions with any tank top-mounted valve will allow for easy removal of the valve for sand replacement down the road.
VALVE SEAT GASKET REPLACEMENT - When replacing the seat gasket, use Hayward adhesive (Part # SPX0710Z9) to seal the seat gasket - otherwise the seat gasket will roll out when the valve handle is moved. NOTE: the gasket is not replaceable on the model 714 multi-port valve.
TANK REPLACEMENT - When replacing a damaged tank, the quickest way to get sand out is to drill four holes in a rectangular about 16" x 10" just below halfway line of the tank, then connect the dots with a reciprocating saw. The opening created will allow for quick and easy removal of sand.
SAND REPLACEMENT - When replacing sand only (not tank), sand removal can be expedited with a wet-dry vac. When refill the tank with sand, cover the upper diffuser or stack pipe so sand does not get inside, and pre-fill the tank with a foot of water to protect the laterals.
TYPE OF SAND - Filter sand should feel coarse; if not, it may be time to replace it. The type of sand commonly used is 20 silica sand, which is neither too coarse (allowing debris by) nor too fine (plugging up the filter permanently)
AMOUNT OF SAND - Sand should be level in the tank, and fill about half the filter. Models vary, but a rule of thumb is to add sand until the top of the sand bed is 12" below the bottom of the valve (or top of the diffuser). The minimum height of the sand should at least reach the widest part of the filter.
RINSE NEW FILTER, NEW SAND - When starting up a new filter or replacing sand, start the filter in the rinse cycle for 1 to 3 minutes to prevent small particles and impurities from blowing back to the pool. If that happens, vacuum the debris to waste
I don't think that a properly sealing strainer lid gasket should squirt. If you have one with a flat lid and the screw downs on the front corners, it could be that the lid, or pump housing is distorted and is not allowing a good seal. There are some excellent threads for finding and fixing system leaks. Good Luck!!!