Add filtersBuilders together

as per this answer: 

https://world.episerver.com/forum/developer-forum/EPiServer-Search/Thread-Container/2016/11/multiple-filter-group/#172178

it appears that filters can be added together when filtering like so... 

.For(query).Filter(filterBuilder | HashfilterBuilder)

but when I try to add them together myself the compiler complains...

myFilterBuilder = myFilterBuilder | (MethodThatReturnsAFilterBuilder());

but the list of filters are going to be dynamic, a user could select any grouping of filters, and we've a central re-usable method that is expecting a single filterBuilder for filtering

How do i add filterBuilders together? Or achieve something that does the same thing?