First keep in mind, its an animal, not a machine. It has a stomach. It can be overfed.
It will then get indigestion.
It will then stop making methane.
You will be able to tell because the gas won't light (it will be increasingly just CO2). The effluent will begin to smell sour (acidic). Your nose will tell you.
At that point you must stop feeding food waste. That will only sour it further. And you should give the poor dragon's stomach some antacid. I suppose you could drop a roll of TUMS in... lots of rolls of TUMS, but that would get expensive! You could use baking soda (sodium bicarbonate, from Arm and Hammer, the same stuff you may put in your refrigerator to keep it from smelling, just be careful, it tends to fizz and froth like your kid's science fair volcano and gets messy). You can use sodium carbonate (Arm and Hammer Washing Powder), that doesn't fizz like the bicarbonate. You can use sodium hydroxide (drain cleaner pellets or fluid). How much? Well, you have to add a little at a time until you get the pH back to neutral.
And then you can ALWAYS add more manure. Manure is a good thing. It reinocculates with methanogenic microbes. It helps balance the pH. It adds some energy that won't sour the tank. Some manures have indigestible stuff that the microbes can live on. You can add manures whenever you want, with impunity. Just know that the more you add the more fertilizer overflow you will have to take care of.
So how do you take care of your dragon?
The rule of thumb for the appropriate 30 to 40 day hydraulic retention time of the solids you put in is to feed the tank no more than 1/40th of its volume. So for a 1000 liter IBC tank you wouldn't put in more than a 25 liter bucket of food waste (mixed food waste and water, usually at about a 50:50 ratio, but since food already is mostly water this is hard to calculate. Just grind up about a bucket worth of food at a consistency that you can easily pour in).
In practical terms this means about one 5 gallon paint bucket filled with a slurry of food waste per day per 1 ton tank. Do the math if you have a larger tank or a smaller tank. 1/40th the volume.
You can always feed less with no problem. In fact the tanks can go months and months with no feeding at all. Mine have recovered for over half a decade from up to half a year of complete neglect and 6 total freezing events. Just know that when you start feeding again, take it slow (like start with a cup or two a day and work your way up to that full bucket) so it doesn't get indigestion as the microbes recover from their slumber. So there is no minimum on feeding. And you can always put in manure at any time. Did we already say that?
You can wait a week and feed your digester only once a week but you can't feed it a full week's worth of food in one go. It is a stomach. Of an animal. An artificial animal to you, but to the microbes who live in your tank well, they think they are still in the cow or horse they came from. Go easy. They can handle about a bucket every 24 hours or so. And it really helps if it is warm.
Don't shock your microbes. They hate getting hot and bothered and then cold and bothered and then hot and bothered. Try to keep their home a constant 20C to 40C averaging 25 to 30. Body tempertature is ideal but hard to acheive in practicality. The tank size helps... they buffer temperature swings a bit.
Do warm water feeding. Keep your tanks well insulated. Heat as necessary. Try to make the microbes happy.
Every time you feed you will get an equivalent amount of liquid organic fertilizer out. Use it with your aeroponics or hydroponics or in your garden or on your grass and trees and shrubs, or simply let it go down the drain. Or you can capture it and use it to grind up the next batch of food and recycle it back into the tank. Give it to your neighbor to start their biodigester. Collect 1000 liters of it and make another 1000 liter digester that will start right away. Oh the possibilities!
There isn't much maitainance to do with the gas. Store it in a gas bag or an air mattress or a floating drum or whatever you want (inner tubes from trucks or tractors stack nicely). Use it whenever you have enough (enough is usually 500 liters which gives you an hour of cooking or so; a tractor inner tube can usually store 60 to 80 liters).
The gas can be stored for millions of years. It won't go bad. Yeah... its natural gas. (Well, that depends on how long your storage bladder lasts, but you could technically keep moving it from storage balloon to storage balloon for the next million years or so...)
If you don't feed the tanks they will stop producing gas, so if you go away, you don't have to worry. Just leave about 1000 liter bag attached to collect what the last bucket of food waste you put in creates if you fed it just before leaving the house. If it makes a little more it will safely burp out the other side (the slurry out tube). And since the CO2 part (30% or so) is heavier than air and falls and the methane part (70% or so) is lighter and floats away and disperses quickly, you are okay.
There isn't much cleaning to do if the system is working right. Occasionally you may find that you didn't grind your food well and some of it floats up and clogs the pipes. So remove the top of the pipe where the fitting is (we don't glue them for this reason) and shove a stick down and unclog it.
If you used a ton of manure with a lot of straw in it you may get a scum layer on top after a few months that impedes the gas from getting out. In that case you may have to open up the IBC lid (unscrew it), reach in and shovel out the scum layer and reseal it. No biggy. We've done it several times. No, there is no worry that while you open the tank you can get hurt. Just don't lick your fingers.
Hope that helps you understand the feeding an maintainance of your dragon.
Okay, I've got my domestic dragon. How do I care for it?