We use a small metal syringe (50ml - 1.7 oz) with an attachment for enemas. The back part of this syringe can be unscrewed so that thick lubricant can also be filled in. Thin liquids can be slowly sucked up using the nozzle.
Before a long rubber colon tube is inserted, we inject a filling of lubricant into the rectum. I also get one or two fillings with it before extensive strapon play. Then everything works as it should...
This syringe is easy to clean. It's better than plastic syringes.
Just search the internet for “ear syringes”...
Below are a few examples from German-speaking countries:
https://www.ebay.de/itm/294917491090?hash=item44aa73c992:g:eE0AAOSwyetkRibJ&amdata=enc%3AAQAIAAAA4MMqPUY8JOlC4ooE7xBriohsaGuEEai%2FYjshttVnQnpSsF2zU7deB%2FLxsmoZdCPewq4UtffCriUTNo6mLST%2FXmRATGHg8scPoHKlVkrevGepPUcOJBo6H01wWaFdz3UlqMLdAJk4BsFPBVeMwu6nfwMjamwG1l%2FjKTv1RL7Y4fyXoWf0GRIeceelD7NMzRmR0Vjmm8K695VM%2Bit%2FHiBMsSWFPkevA5YcuVYmeNbHVwtzb8J%2FOjjgwm8M9xdu4nMJ1Uy2LR5e3N%2FGBJZEeJ92FznUoekcLTi4b1b1%2Ff4t8ZEu%7Ctkp%3ABFBM6q-W9vNi
https://www.ebay.de/itm/394626405258?hash=item5be191138a:g:6V8AAOSwgW1kYjmg&amdata=enc%3AAQAIAAAAwAMOurWeDsgTWYGHt%2FEUhauPiZu0w%2FGv2b91obrJWWnZnvRxtatUu2UsFe2ystFJpTaH00hwlR2mcbbrQfLai6ns7cP6wYFLLGZU90yLMG%2FH2I1t1%2FbRh2FUyRJMNm%2FFGLjvyr4F%2FhHs3l%2FkDPBOIo6UtEC3tcUql3bdHlqkYlwdCe%2Fj6z%2FQnL38Iz7KTUDdf4PZ6owbXIHfpiKWcPZJhkT2PQBW9p4Yy3HCZQ6VNncGr%2BNOH%2F8NHZUpKEpxtUy8RA%3D%3D%7Ctkp%3ABk9SR6qI2PbzYg
https://www.instrumentenrw.de/Beauty-Handinstrumente/Ohrenreiniger/Ohren-Reinigung-Set-Rostfrei-Ohrenspritze-50-ml-Ohrenreiniger-13-5-cm-Nierenschale-15-cm-fuer-die-Ohrenreinigung-zu-Hause-oder-Unterwegs::3256.html
https://www.ebay.de/itm/154391725423?hash=item23f276c56f:g:khsAAOSw3XNgXxja