Re: pooling water at outlet

RM,
Sorry to say this, but a 750 gal tank with only 1 leach line is totally inadequate. You should replace it with a new tank 1500 or more gallons with a minimum of 2 compartments. 3 compartments is best.
http://www.deihlprecast.com/html/septic_tanks.html
It should also be installed with risers above the tank and above the D-Box to make it serviceable in the future.

The best options today for the drainfield leach lines are called the infiltrator:
The Chamber system does not need a rock & gravel bed & highly recommended by most pros.
http://www.septicsolutions.net/store/Infiltrator.htm
Demonstration for the Infiltrator Chamber system.
https://www.youtube.com/watch?v=He6CAQr8X6E
You can order the infiltrator from Septic Solutions:
http://septicsolutions.com/InfiltratorChambers/InfiltratorQuick4.html

You might be able to get your single leach line running again by hydro-blasting it, but I'm afraid it will soon be giving trouble again. How many people live in your house?
See my reference file for hydro jetting the lateral pipes.
https://docs.google.com/document/d/1HL-0iahk8hPwqclnajsgFnaDEq6JGNMZLaCZ14c2rps/edit#

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