How do you do that? (really asking)
Not sure if TriPolar is talking about actual leaks, or when the toilet will not stop running. I have one toilet that will not fill up the tank if the flapper valve does not fully seal. And frankly, it’s a pain in the ass.
Really, if a house is not to be occupied for a while, turn off the water. Simple solution. Problem solved. I do this at my home when I go on vacation, and at my mothers home. She is no longer with us, and my brother and I are looking after the house until we sell it.
I also installed 4 cameras on the house that was actually quite easy. I can look at it anytime I want on my phone.
This isn’t merely a good idea–it’s vitally important.
My first reaction when I read the Op wasn’t to think about the evaporation issue. I was more surprised at the concept that he was planning to leave the house unoccupied and unvisited for half a year
A lot of very bad things can happen. Storm damage, broken windows, animals like raccoons ,whatever.
I would install cameras inside and outside the house.
For a flapper leak the easiest way is to get one of those Tidy Bowl type things that turns the water blue, install it in the tank, don’t flush, and wait. If you see blue water in the bowl your flapper is leaking. Otherwise, shut off the water supply to the toilet, flush it, get rid of as much water in the bowl as possible, then fill the toilet tank with water and wait. If you have a flapper leak all the water will slowly drain into the bowl. If you have to shut off the main to do this fill up your bathtub or something ahead of time with enough water to fill the tank, then put “Install shut off valves” on your to-do list.
To look for other leaks in the toilet use oil or plastic to stop evaporation with the bowl full of water and wait to see if the water level in the bowl goes down. That only tells you if there’s a crack in the bowl or leak in the tank that drains into the bowl. To find anything else you need a visual inspection of the drain pipes the leaking water.
Also check all your supply plumbing occasionally. Don’t use any water and check your water meter after an hour, then 24 hours or longer if you think there is a leak in your supply pipes. If the meter doesn’t change in 24 hours it’s really slow leak. If you have a boiler for hot water or steam you could be losing water through float valves and steam outlets so do this when you don’t need the heat on. For most hot water heat you could close off the autofill valve for a day but never do that on a steam boiler.
Yeah. The house gets visited about 4 times a month. Sometimes I stay for a week at a time. My brother also does a security check. It’s good that activity is somewhat evident having people come and go.
I have two inside, and two outside cameras that cover most everything (single floor only 1000 sq ft).
It gives me a bit of piece of mind. I can make sure the grass is getting mowed and the sidewalks shoveled in winter. See if there is a bunch of flyers stuck in the front door. It was only about $250 bucks for the set up, and I think $10 a month.
I opted out of the extra cost to alert the police when ever motion is detected. What are they gonna do, arrest the mailman?
The cameras alert me though, when they detect motion.
It’s a challenging situation. My wife and I live in the US, but the house is located in rural Japan, making it very difficult to visit more often than once or twice a year.
Most of the neighbors are assholes who are not to be trusted, and we can’t find a property management company that’s willing to drive that far out into the countryside to check the house inside and out and arrange for any required emergency repairs. We’re looking into a security company that may be able to do a monthly walk-around outside the property and send us a report, though I’m not sure what we’ll do if e.g. they tell us there’s a broken window.
We do have a camera inside the house, and we’re considering adding another outside.
From what I’ve read, automotive antifreeze causes problems with septic systems, though not particularly with municipal sewer systems. Ethylene glycol is toxic to mammals, so there’s a safety issue associated with using it in toilet bowls that pets might drink from. In the past, pouring antifreeze down the toilet was standard advice, but I see that’s no longer the case. Propylene glycol (used in RV/plumbing antifreeze) is much less toxic.
Why not just use enough oil that it would fill the trap completely? That would eliminate all the possibility of evaporation.
However, is mineral oil the right thing to use? Why not vegetable oil or something else not quite so non-biodegradable?
Presumably because you don’t want it to biodegrade while it’s parked in the toilet bowl for several months.
It might be difficult to completely full the bowl with oil. The more you pour in, the more water it pushes out the other end - until the oil level is low enough to sneak across the top of the trap, above the water on the bottom of the bend, and from then on you’d just be pushing oil down the drain while leaving a quantity of water at the bottom of the trap. Might still be worthwhile, because at least then you’d have an oil film on both sides of the trap, blocking evap from the upstream and downstream ends.
That’s what I’m getting at- you could basically keep the water in the trap from evaporating if you put enough in.
If you’re looking for a light mineral oil that smells nice, try baby oil. I switched to that instead of standard honing oil for sharpening tools. it does the job just as well and doesn’t stink the place out
I’m trying to figure out what the problem is. So what if it evaporates? Is this a concern with sewer gasses?
Not sure of toilet designs in Japan are. I would think a tight Saran Wrap over the bowl would certainly help.
And oil is a darn good idea.
Sewer gas is one concern. Apart from stinking up the place, sewer gas can be toxic and explosive.
The other concern is that if a trap or toilet bowl dries out, it creates a path of entry into the house for sewer-dwelling cockroaches.
Maybe you could get George Costanza to exercise the toilet gaskets. 
I think you are on the right track with the baby-oil, you just need to delicately flush (or “agitate/disturb”) the traps, to get some of the oil behind the lowest part - so that the oil will rise on both upwards legs of the “U” - and seal both sides.
just pouring the oil in and then walking away will not get it to the other side.
that is probably your safest bet
Yeah, when I had to remove one of my toilets for problems for a week or two, I stuck a rag in the toilet drain and poured water on it every day to keep out any fumes/gas.