Sixty-three trucks a year
The defaults describe an ordinary occupied house on a holding tank: a 1,000 gallon tank with the alarm at 75 percent, the truck leaving it at 5 percent, and 120 gallons a day going down the drain. That is 700 gallons of working volume, which lasts 5.8 days. Over a year the house sends 43,800 gallons into the tank, which is 63 visits at 285 dollars, or 17,955 dollars.
Divide it out and a gallon down the drain costs 41 cents. The same gallon out of the tap costs 0.6 cents. It is 68 times cheaper to buy the water than to get rid of it, and that ratio is the single most useful thing on the page — it is what makes a dripping toilet on a holding tank a genuinely expensive fault rather than an annoyance.
The bill follows the trips, not the gallons
The whole 285 dollars in the default case is the flat charge; the tank only gives up 700 gallons, well under the 1,500 the charge covers. So 800 gallons of paid-for capacity leave in the truck as air on every visit — 50,400 gallons a year of allowance bought and not used. The effective rate is 40.7 cents a gallon against 19 cents if the load went out full.
That is why the saving from using less water arrives in steps. Cut the flow by ten gallons a day, from 120 to 110, and the year goes from 43,800 gallons to 40,150 — from 63 visits to 58, and from 17,955 dollars to 16,530. The 1,425 dollars saved has nothing to do with the 3,650 fewer gallons and everything to do with the five trucks that did not come.
The number to know before you need it
When the alarm sounds there are 250 gallons of headroom left, which at 120 gallons a day is 50 hours. On a peak day at 168 gallons it is 35 hours and 43 minutes. That is the window in which somebody has to answer a phone, and it is a different figure on a Friday evening in a rural county than the average suggests.
Everything in it assumes the house carries on using water at the rate entered. In practice the first thing that happens after an alarm is that the household stops, which extends the window by an amount no calculation can predict and no household should have to rely on.
What the arithmetic leaves out
Winter access is the big one. A truck that reaches the tank easily in June may not in February, and a haulier who cannot get down the drive charges for the trip anyway. Then there is the alarm circuit itself, which is a standing cost and a single point of failure; a float that has stopped moving turns a 50 hour warning into no warning at all.
None of the tank sizing, the alarm level, the permitted use of the system or what may be done about any of it is decided here. A holding tank exists because a site could not take a conventional system, the size and the arrangement come out of a permitted design, and altering any of it is a permit matter. This page multiplies gallons by rates.
Questions people ask
How often does a holding tank need pumping?
Working volume divided by daily flow, and it is brutal. A 1,000 gallon tank with the alarm at 75 percent and the truck leaving 5 percent behind gives 700 usable gallons, which at 120 gallons a day is 5.8 days. A full-time household on a holding tank is looking at a truck roughly every week, all year.
What does a holding tank cost per year?
On the default figures — 63 visits at 285 dollars — it is 17,955 dollars, or 41 cents for every gallon that goes down a drain. Your own numbers will differ, but the shape of the answer does not: it is dominated by how many times a truck has to come, because nearly all of the charge is for sending it.
How long do I have once the alarm sounds?
The space above the float divided by the flow. With the alarm at 75 percent of 1,000 gallons that is 250 gallons of headroom, which is 50 hours at 120 gallons a day and just under 36 on a peak day. It assumes the household carries on using water normally, which is the assumption that usually fails in your favour.
Will using less water save money?
Only when it removes a whole truck visit from the year. Ten gallons a day off the default case takes the year from 63 visits to 58 and saves 1,425 dollars — real money, but it arrives in steps of one visit rather than smoothly. A change of two gallons a day may save nothing at all until it crosses the next boundary.
Would a bigger tank be cheaper?
The arithmetic says yes, because the flat charge dominates and a bigger load spreads it further. Whether it is possible is another matter entirely: tank size on a holding tank system comes out of a permitted design for a site that could not take a conventional system, and altering it is a permit question rather than a shopping one. The page shows the figure so the conversation can start from it.