Inside vs. Outside Drops

[SGleason]

Hoping someone can answer this for me as I'm having trouble getting a solid answer. What is the reason for choosing an outside over an inside drop at a sanitary manhole? Are there scenarios where one is more appropriate?

 

[bimr]

Outside drops are a little more expensive.

Inside drops are generally less preferred because material may hang up on them, inside drops are generally not as sturdily built as an outside drop and they may break, inside drops make it more difficult to clean the sewer and manhole, and the inside drops take up space inside the manhole in the event that you want to want to clean or enter the manhole.

 

[jkamerer]

Check your local jurisdiction/municipality, I have worked in different jurisdictions where they preferred one over the other. As stated earlier it really comes down to maintenance.

 

[rconner]

While most are probably aware of this, ASCE MOP 60 (old WPCF MOP FD-5) advised at least years ago that drops should for various reasons (e.g. susceptibility to blockages etc.) be used only "sparingly", or where it is not economically feasible e.g. by gentle vertical curves etc. to steepen the entering sewer.
While traditionally I believe many exterior drops are indeed more expensive to construct e.g. required to be encased in concrete etc., an exterior arrangement has an arguable potential advantage that by running the vertical part of the riser with a pipe all the way to the surface (as by use of a cross fitting at the top) and there provided with a smaller separate cover that would not transmit surface loads (not unlike the principal of a valve box), a clogged drop might be cleaned if ever necessary from the surface, and without having to enter the confined space etc. [It would appear also without major modification to standard utility manholes, cones and covers etc., either.]