Marcos I wouldn't sweat on this if I were you. As I said earlier the fine from the EU for non-compliance is a one off one of €2.7 million, with a daily fine of about €26K+.
This equates to around €9.5 million per annum, the other side being probably bringing in a new septic tank inspection department say one inspector for every two thousand tanks would cost just as much and more.
Couple that with say €7000 cost per tank and multiply it by 200,000 pre 1980s tanks you would get a cost of €1.4 billion. Probably a government grant of 40% towards new tanks would cost €560 million.
€560 million would pay the EU fine for the next 60 years ! Actually if the government were

to just accrue the interest they would have to pay on this amount it pays them to pay the fine.
Not to mention the cost of hiring 200 septic tank inspectors which with travel and the fact that they would have to be environmental engineers would probably cost minimum €40K per head or another €8 million a year.
No contest, this is one where a committee will be formed, a report will be produced, and no more will be said about it. We will happily pay our €9.5 million to the EU every year and that will be that.