Like Sailak said, the most common hose sizes are 3/4" intake and 1-1/2" discharge. Some electric toilets use a 1" discharge as they have built in macerators.
Raritan makes a super flexible hose that is warrantied for 5 years against odor permeation. Trident also makes a five year hose that is less expensive but not as flexible.
The following is from the Raritan website.
NEW - Sani/Flex Odor Shield Hose
Tired of smelly, clogged hoses?
Highest Quality marine Sanitation Hose. Uses Butyl rubber construction which has the lowest odor permeation level not found in other rubber or PVC material hoses. Extremely flexible for easy installation with a low bend radius up to one time its diameter.
5 Year warranty against odor permeation.