Can the outlet pipe of the grease trap be connected to the horizontal pipe of the toilet waste water

It must be separated. The bathroom kitchen sewer pipe can not be connected, otherwise the smell will be flushed up by the pipe when cooking and flushing in the bathroom, the reason is that the drain in the kitchen is higher than the bathroom drain, and the toilet in the bathroom has an anti-odor curve, while the kitchen does not.

There is no very clear distance regulation, but because the flue temperature is extremely high when the water heater is used, it is recommended to keep it above 30cm, and if the distance is not enough, the effective separation of thermal insulation materials is used.

If you have an electric water heater, you don't need a hot water pipe, you can take a shower with a hose directly from the water heater.

It's easier to get annoyed like this. Because of the garbage drain in the kitchen! It's easier to connect them if you don't want to, but they won't. It doesn't necessarily have to be blocked.

Try to bury it as much as possible, otherwise it will affect the appearance.