Bacground info as follows: Bought my house last year... built in 1917... they added a 40,000 gallon cement pool in 1952... records show cement on the bottom is 5 feet thick... very well constructed and has held up well throughout the years. House sat unsold for 2 years... pool was not used for at least 3 years... we have spent $10,000 on repair of pool structure (added skimmer, etc.), painting, and on and on... Though very highly recommended, our pool guy is a bit of a flake and it is still not open. Added a Salt Water chlorinator, etc., and asked him if he cleaned the filter... he said he was "afraid to open it". Now I cannot "open" the pool with a clear conscience... can't yet find someone to check it for us... would like to service it ourself if possible. Alot of info is "worn off" the unit but it is a pressurized Triton MSF cert High Rate sand filter for swimming pools for residential or public use... also says pac-fab, and uses silica sand and pea gravel... it is pressurized... it hasn't been cleaned or opened for at least 3 years... any thoughts????