Thank you for the question. If this is agreed between parties you don't need to put anything in a legal context, however if. you wish to do so then you can change the title deeds to show an easement on the land providing for the refuse disposal. This means that if you were to sell the house in the future, then neighbouring property wold continue to have a legal enforceable access to that land. You would want to look at a conveyancing solicitor to draft the easement for you and register the same at the land registry.
I shall provide you with a helpful link that will assist you in finding a solicitor/representative near your local area. This will provide you with someone nearby your area who can assist you if required.
I hope this information proved helpful. You will find a local solicitor who deals with these matters on the law society webpage which is as follows;
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