Fire the Maestro. In my exp the majority of people who do septic systems either don't know how they work or pad the amount of work needed. Why do a job for $500 when it's just as easy to charge $7000 for a whole new system?
I would have someone
reliable check out your current system before digging a new one. A
proper septic system shouldn't ever flood into the house, even when the system fails.
It is very unlikely the tank itself is failing and it's far more likely there is a design problem that can be fixed with hand-digging. When a septic system fails it should be from water perking up through the leech field into your yard. Tanks can always be pumped out and modern ones should last well over 50 years(or much more). They are made from concrete, not cardboard.
Some questions to find out:
Has the tank ever been pumped out? This is usually a good first step.
Does the line going into the tank go in a direct line from the house? There should be no angles or mysterious boxes. It should be level or on a downward grade. I've seen septic system that have pipes that go uphill a few inches into the tank. This can cause problems...
Is there a leech field, or is the tank simply a "dry well"
Have you ever had a "perk test" on your soil? If you have a leech field in clay, a new septic system will simply be a waste of time and a lot of money.
What kind of soil is there in the leech field? Doe the tank back up more when it rains?
A properly installed leech field will have perforated pipes with the holes going down only. Some pipes are installed improperly. There should be 12"-18" of gravel under the pipes.
Are there any trees that could have roots infiltrating the septic lines? In the US Willow trees are notorious for doing this, but I don't know about the tropics.
Are there proper baffles on the tank? A septic tank should have an outgoing baffle so that any waste going to the leech field comes from a foot or two below the surface of the waste water. This is typically made from 4" PVC pipe made into a sideways "T." Without this baffle, your outgoing pipe is subject to plugging from TP and solids.
Is there access to the outgoing baffle?
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The most important thing is to a perk test. Have someone dig a hole about 5 ft deep in your leech field and see how long it takes for five gallons of water to drain into the soil. It should take no more than 8 minutes to drain. If it is clay or other non-porous soil, you will need to put in a sand filter, which can be quite costly, or if you lucky, you may be able to extend the leech field to more porous soil. If there is no gravel in the leech field, you will need 5-10 cubic yards of gravel under the pipes to help the field filtrate into the ground. Make sure the leech field pipes are level.
There is no reason to replace the tank if the problem is the leech field. None. When I was a teenager in the US I
handdug a new leechfield in a few days. Four feet down and sixty feet of leech field. You should be able to find a half dozen Haitians who can do the work in the DR for a $100 or so.
What my dad did with his systems was to build boxes around the access holes out of pressure treated 2x6s on one side and 2x8s on the ends. Then there was a lid made from 2x6s that was a few inches under the soil. It made finding the tank easier and saved a lot of digging when it had to be pumped or inspected.