Brian,
Another way to do this without excel is to use activity steps (if using Primavera).
Create one activity with duration of 50 days.
Add activity steps for each item & set activity weight (can all equal 1 if all items are the same, or can all be set different if required).
As the activity steps are updated, the physical % complete is updated based on weight.
Means using Physical % complete instead of duration % complete, it can run a global change to set duration % complete = physical % complete. Resources are only assigned to the task not the steps.
Regards,
Steven

I like Tom Boyle’s approach, no need to use dummy resource loading that can be error prone.   I can do it as Tom Boyle suggests with Spider Project if using a UDF and a Script to take control of how field values are rolled-up.  After UDF and Script are defined then after any update schedule all I need is to run the script with a single click of the mouse to get it right. Click F10 after defining the script as favorite, a step left out for others to see a script is being used. Because I record my scripts as if a macro recording everything is easy, no need to manually enter script commands. Tom is right when he says best procedure depends on the software. 

I believe Tom’s approach is less prone to error than some of the other methods that may also work.  If using LOE activities or dummy resources missing to include the correct LOE links or missing to resource load any new activity will get it wrong.  For P6 the use of WBS summary type might do the trick but I expect it to work at a specific WBS element, but a single schedule might have hundreds of WBS elements, therefore it is possible Tom’s solution is still the best for P6.

Mr. Cognac, The easy way (as Tom said), is to do it in Excel. You can paint your summary line to span 50 columns, and make a list of your tasks underneath. Then you create a formula that make your task vanish once completed, and also one span of your painted column vanish correspondingly as well. And EUREKA! once all tasks are completed, then you got a clean spreadsheet!

Zoltan, maybe I mis-read the question.  It would be nice for the OP (Brian Hennessy) to re-join us and clarify his intent.

Raymund, my knowledge of resource leveling is not at issue, nor is yours.  For his very first post on this site, the OP asked for assistance on aggregating the durations of 50 individual, unscheduled “tasks” into a single “summary duration” or “summary line item.”  He…

1. …did not mention P6 or any other scheduling software (though the repeated references to “tasks” suggests that P6 is not his tool of choice);
2. …explicitly stated that he has NO interest in scheduling (or sequencing) the work;
3. ...used no schedule-related terms (e.g. start, finish, predecessor, successor, constraint, deadline, float…) other than “duration;”
4. …made NO mention of resources or anything that might be construed or modeled as a resource.

My advice to the OP may have been no better than yours or Zoltan’s.  In hindsight, I’d suggest that he enter his 50-task checklist into an Excel spreadsheet with columns for OD and RD, and a summation formula at the bottom of each column. Done.

no leg pulling straght up 

Asuming you are using P6.

Use the Levelling of Resources.

What software do you use?

It makes sense to put such questions in the forum on your software.