Method
As with singing through the instrument, it is possible to amplify yelling/shouting through the tuba and euphonium.
Necessary information
Vocal effects have a tendency to lose articulation when projected through the tuba and euphonium, due largely in part to the restrictive effects of the mouthpiece opening. This can be mitigated in largely the same way as vocalizing, i.e., by allowing part of the mouth to slip out of the mouthpiece rim during performance. It is also beneficial for the performer to overly enunciate each word; the conscientious performer will do this as a matter of fact.
Although not specifically tied to the use of this technique with the tuba and euphonium, care must always be taken to ensure that the performer doesn’t have to yell or shout to the point of damaging the vocal cords. Additionally, some performers may be uncomfortable with using such a technique; when writing with this technique, it is highly recommended that you check with the performer to ensure that they are accepting of such musical demands.
Notation
Screaming/yelling effects can be simply notated, either with simple words and directions printed above the main staff, or paired with its own staff and rhythmic notation (a la Sprechstimme). Other than that, the notation guidelines for the Singing section apply here.
Works to consider (bolded titles are particularly representative examples of this technique)
19 E. Main St., Alhambra, CA 91801 – Nicholas Deyoe
Solo Tuba Music – Cort Lippe
SVPER-ANGRY DEATH-BLAST ASSAVLT COVNTDOWN III – Francis Robert
The Composer's Guide to the Tuba 