When I began in the hobby I had an online friend who had been in the pet and fish business for over 50 years. He had owned stoed, worked for others, done imports and even worked in breeding. By the time we met he was retired and just a hobbyist. He use to tell me he hated hoses. The would leak, the would let go they were a danger as far as he was concerned.
I took him at his word and when I got my fist canister and with every hosed device since I have used mostly stainless steel hose clamps. For smaller hoses used in air driven systems I use the plastic style clamps in dougall's pic.
You can find hose clamps in assorted sizes in pretty much any hardware or building supply place.
On my canisters I also have inline heaters. So I clamp them as well. I also clamp the connectipns where the hoses from the filter attach to the spraybar and the intake. I only use Eheim Pro II cainsters which are about 20 years old and have been at least twice replaced by newer lines. The fact that my oldest one has been running for over 20 years and is still as quiet as the day I bought it explains why I chose Eheim. I have three running, one for spare parts and then the larger sized one I never managed to put into use.
If you issue is nit with air sneaking ni via hose connections, then I would look to the head gasket. That is the one which seals the top and body of the filters when the unit is closed. I usually take the gasket off and rinse it when I clean my filters every 6 months. If that gasket degrades, it can cause leaks of water out and.or air in.
Finally, AFter I have cleaned the filter I refill it fully and then return it to the tank. Because the filter has shut-off valves, the intake and return hoses remain filled with water when the filter is removed. So when I restart there is little or no air inside the filter. In fact, for the first 10 years I had my first one, I ran CO2 directly into the filter's intake. This was another reason I chose Eheim. Most canisterss do not do well with gas bubbles inside.
