No, not universal, although there are only 3-4 types. Most in North America have 3/8 copper pipe or 3/8 braided hose.
On the firewall, under the hood, you will find the inlet and outlet hoses.
I don't know about the outside diameter of the hoses but, the outside diameter of the heater core inlet and outlet tubes are 3/4" (inlet) and 5/8" (outlet).
It depends on the vehicle you have. In many cases (but not all) the inlet hose is smaller than the outlet hose.
yes
Remove both heater hoses from inlet & outlet of heater core. Connect these hoses together.
Couple inlet and outlet hoses together
Sounds like an air leak in the inlet hoses. check the inlet pipes from the air filter to the inlet manifold for splits
2 - inlet & outlet
join the inlet and outlet hoses together.
2 hoses total, Upper and lower radiator hose. There is also 2 heater hoses, an inlet and outlet hose.
The attachments for portable dishwashers are not universal, and do not fit all faucets. To fix this, a person can buy an attachment for their faucet the matches the dishwasher.
Upper and lower radiator, inlet and outlet heater core, bypass,Upper and lower radiator, inlet and outlet heater core, bypass,